A polymeric solid electrolyte is a kind of polymeric thin film performing ion conduction rather than electron conduction. The polymeric solid electrolyte is adapted to be used in a series of primary and secondary lithium cells or lithium-ion cells to thin the cells in shape. The thinned cells can also be further processed into windable cells, bipolar stack cells, thin-film cells, etc., according to various requirements. In addition, the use of polymeric solid electrolytes in the cells can overcome the problems of difficult package and current leakage encountered by general cells with liquid electrolyte.
In earlier stage, the research on polymeric solid electrolytes is focused on the polyethylene oxide-based material. The material has a relatively low conductivity, as low as 10.sup.-7 .about.10.sup.-8 S/cm, at room temperature so that the material works only at high temperature such as 80.degree. C. or above. Furthermore, a lot of organic solvent which is detrimental to the industrial security and the environmental protection is used and then evaporated in the process for producing the polyethylene oxide based thin film.
In recent years, gel electrolytes, such as polyacrylonitrile (PAN) based electrolytes, have been reported to be used in cells, and the product has a practically desired level of conductivity at room temperature. Nevertheless, the film has to be produced in a glove box or dry room so that the manufacturing process will be built with high cost.
In addition, B. J. Bauer et. al claimed in U.S. Pat. No. 4,654,279 a two phase interpenetrating network, i.e. a mechanical supporting phase of a continuous network of a crosslinked polymer, and an ionic conducting phase, comprising a metal-salt-complexing liquid polymer. The conductivities of these polymeric electrolytes are constrained by the properties of the liquid polymer, which are approximating 10.sup.-4 S/cm, too low to be used in general lithium batteries.
On the other hand, our another invention bearing a U.S. patent application Ser. No. 08/856,725 and filed on May 15, 1997 claims a polymeric electrolyte of a polymer (WPU) film containing an organic liquid electrolyte. Among these electrolytes, WPU plays the roles of mechanical supporting matrix and ions conducting medium. Due to the conflict of these two properties in general, it is not easy to improve both of the conductivity and the mechanical strength simultaneously.